Electronic device and methods for fabricating an electronic device

ABSTRACT

An electronic device and a method of fabricating the electronic device includes forming a first electrical contact, a dielectric layer and a second electrical contact wherein the dielectric layer is located between the first and the second electrical contacts, forming an electrically insulating layer over the dielectric layer and the first electrical contact, exposing the first and second electrical contact, the dielectric layer and a first portion of the electrically insulating layer to radiation from the side of the first electrical contact, removing a second portion of the electrically insulating layer that was not irradiated by the radiation, providing a semiconductor material over a portion of the dielectric layer, and forming at least a third electrical contact over at least a portion of the electrically insulting layer and the semiconductor material.

BACKGROUND OF THE INVENTION

This is a Division of application Ser. No. 10/739,189 filed Dec. 19,2003. The entire disclosure of the prior application is herebyincorporated by reference herein in its entirety.

1. Field of Invention

This invention relates to electronic devices such as, for example,transistors and methods for fabricating the same.

2. Description of Related Art

Electronic devices, such as, for example, transistors, have a multitudeof uses. For example, low cost, large area arrays of thin-filmtransistors (TFTs) are important components in flat panel displays,electric paper, and imagers. In a pixel of a display, a TFT is used asan electrical switch to charge a pixel electrode that switches thedisplay media from one state to another. A display backplane comprisesan array of pixel elements that is used to address the display media.Amorphous silicon is often used as the active material in TFTs for theseapplications.

Polymeric semiconductors have field effect mobilities of approximately0.01-0.1 cm²V⁻¹s⁻¹ and are relatively simple to process due to theirsolubility and ease of forming continuous films. These field effectmobilities are typically lower than those obtained for amorphoussilicon, ˜0.5-1.0 cm²V⁻¹s⁻¹.

Additive and subtractive patterning techniques are sometimes used tofabricate patterned polymeric TFTs. Additive methods deposit only enoughmaterial for the desired pattern while subtractive methods deposit ablanket layer of material and remove the majority of it to define thepattern. Two subtractive methods for organic TFTs includephotolithography and screen printing. Photolithography is ahigh-resolution, subtractive method for patterning, and is sometimesused to make complex circuits and displays with organic materials. Anadditive method sometimes used for fabrication of organic light emittingdiodes, metal-organic-metal diodes, and TFTs is inkjet printing. Inkjetprinting sometimes maintains registration by digital-image processingand precise spatial control of deposition.

Generally, in a transistor, the source pad and the drain pad areconfigured in coplanar geometry. That is, the source pad and the drainpad are positioned over the gate electrode and under the semiconductor.Also, the source pad and the drain pad are sometimes configured in astaggered geometry. That is, the source and the drain pad are locatedover the semiconductor.

SUMMARY OF THE INVENTION

The use of organic semiconductors can have advantages over amorphoussilicon, especially for flexible electronics. Organic semiconductors aresometimes processed using low-cost techniques, are sometimes depositedat the low temperatures (e.g., lower than 150° C.) required for plasticsubstrates, and tolerate mechanical stress. The development ofmicron-scale processing techniques for organic semiconductors is alsobeneficial.

The use of organic semiconductors in TFTs in backplanes for displays islimited by their lower field effect mobility relative to amorphoussilicon semiconductors. A TFT in a pixel element in a backplane providescurrent to place charge on a pixel electrode that causes a change in thedisplay at that pixel. The existence of injection barriers at thecontacts of organic TFTs can limit the maximum possible output currentof the device and thus increases the time needed to place charge on thepixel electrode. In order to solve this problem, and to achieve thecurrent required to charge a pixel electrode in a typical display, theelectronic device, such as, for example, the transistor, is enlarged.This enlargement decreases the fill factor of the pixel in the displaybecause of the increase in spatial area of the TFT in the pixel element.

The output current of the some organic electronic devices, such as, athin film transistor, depends on the geometry of the device due to thepresence of injection barriers at the source and drain contacts. Deviceswith staggered geometries can have larger output currents than deviceswith coplanar geometries due to decreased contact resistances. However,the manufacturing of devices with coplanar geometries is easier than themanufacturing of devices with staggered geometries, and is preferred fordisplay applications.

Another problem commonly associated with organic devices such as, forexample, transistors, is the type of material used as a via layer. Thevia layer reduces capacitive coupling between the addressing electrodesand the display media. Some via layers require processing steps, such ashigh temperature or reactive ion etching. These processing steps candamage the organic semiconductor.

In various exemplary embodiments of the devices and methods according tothis invention, an organic electronic device is fabricated in a geometryto reduce the injection barrier at a contact. This allows a higherpossible output current of the device.

Various separable exemplary embodiments of the devices and methodsaccording to this invention have one staggered contact. This allows fora larger output current without necessarily enlarging the TFT. Thus, thequality of the image on the display experiences reduced degradation.

In various separable exemplary embodiments of the methods and devicesaccording to this invention, an thin film transistor includes a gateelectrode, a drain electrode, a source electrode, a via layer, anencapsulant, and a gate dielectric layer on the gate electrode, whereinthe source and drain electrodes are over the gate dielectric layer, andwherein a semiconductor is in a recess of the via layer and is over thegate dielectric layer, and either the source or the drain electrodedepending on the electrical biases used to drive the TFT.

In various separable exemplary embodiments of the methods and devicesaccording to this invention, a semiconductor is formed in a recess of avia layer by printing, a drain pad is a metal electrode formed over aportion of the via layer, and an encapsulant is over the semiconductor.

In various separable exemplary embodiments of the methods and devicesaccording to this invention, an encapsulant planarizes the electronicdevice.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, the electronic device includes an organicthin-film semiconductor.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, the via layer has a tapered side.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a gate electrode, a dielectric layer and asource pad are formed wherein the dielectric layer is between the sourcepad and the gate electrode.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a via layer is over a dielectric layer anda gate electrode.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, the electronic device is exposed toradiation from a gate electrode side.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a portion of the via layer that was notirradiated is removed.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a semiconductor is formed on a portion of adielectric layer that is not covered by a via layer.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a mask is formed over a source pad and aportion of a semiconductor.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a metal electrode is formed over a vialayer, a semiconductor and a mask, and the mask and metal over the maskis removed.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a semiconductor is printed on a portion ofa dielectric layer that is not covered by a via layer.

In various separable exemplary embodiments of the devices and methodsaccording to this invention, a via layer is formed with a tapered edge.

These and other features and advantages of this invention are describedin, or are apparent from, the following detailed description of variousexemplary embodiments of the systems and methods according to thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of devices and methods according to thisinvention will be described in detail with reference to the followingfigures, wherein:

FIGS. 1-3 are cross sections of electronic devices;

FIG. 4 is a cross section of an exemplary embodiment of an electronicdevice according to this invention;

FIG. 5 is a cross section of another exemplary embodiment of anelectronic device according to this invention;

FIG. 6 is a cross section of another exemplary embodiment of anelectronic device according to this invention;

FIGS. 7-13 are cross sections of another exemplary embodiment of anelectronic device illustrating an exemplary embodiment of a method ofmanufacturing an electronic device according to this invention;

FIG. 14 is a cross section of another exemplary embodiment of anelectronic device according to this invention; and

FIG. 15 is a flow chart describing an exemplary embodiment of a methodof fabrication of an electronic device according to this invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1-3 show illustrations of electronic devices 100, 120 and 130. Adielectric layer 108 is formed over a substrate 110 and over a gateelectrode 109, and a semiconductor 106 is formed over the dielectriclayer 108. In FIG. 1, an electrode 102 and an electrode 104 are locatedover the semiconductor 106. In FIG. 2, an electrode 122 and an electrode124 are located between the semiconductor 112 and the substrate 110. InFIG. 3, an electrode 132 is located between the semiconductor 136 andthe gate electrode 110, and an electrode 134 is located over thesemiconductor 136. When electrode 102 and the electrode 104 are locatedover the semiconductor 106, such as in FIG. 1, for example, theelectronic device 100 is said to be in a staggered configuration. Whenthe electrode 122 and the electrode 124 are located between thesemiconductor 112 and the gate electrode 110, as in FIG. 2, for example,the electronic device 120 is said to have a coplanar configuration. Whenthe electrode 132 is located between the semiconductor 136 and the gateelectrode 110, as in FIG. 3, for example, the electronic device 130 issaid to have a hybrid configuration.

Typically, devices with staggered geometries, such as FIG. 1, forexample, can have larger output currents than devices with coplanargeometries, such as FIG. 2. However, an electronic device 120 with acoplanar configuration, such as FIG. 2, for example, is sometimes easierto manufacture than an electronic device 100 with staggeredconfigurations, such as FIG. 1, for example. Thus, an electronic device120 with a coplanar configuration, such as FIG. 2, is sometimes enlargedto compensate for the lower effective mobility. The enlargement of acoplanar electronic device 120 at a pixel reduces a fill factor of thepixel, thus degrading the image of the display.

FIG. 4 is a cross section of an exemplary embodiment of an electronicdevice according to this invention. Some of the elements in this figureare commonly numbered with elements previously discussed in connectionwith other figures. A duplicative discussion of those elements isomitted for the sake of simplicity.

An electronic device 140 has a hybrid, i.e., both coplanar andstaggered, configuration. Thus, in various exemplary embodiments, anelectrode 143 is formed over the dielectric layer 108, and asemiconductor 146 is formed over a portion of the electrode 143 and overa portion of the dielectric layer 108.

In various exemplary embodiments of the devices and methods according tothis invention, a solution processable semiconductor 146 is printed overa portion of the electrode 143 and the dielectric layer 108. In variousexemplary embodiments of the devices and methods according to thisinvention, an electrode 147 is a metallic electrode formed over aportion of a via layer 144 and in electrical contact with an electrode149 which is located over the semiconductor 146. In various exemplaryembodiments of the devices and methods according to this invention, theelectrode 147 and the electrode 149 are made from the same material andform a continuous single electrode. In various exemplary embodiments ofthe devices and methods according to this invention, the electrode 147and the electrical contact 149 are made from a different material andare thus physically distinguishable. In various exemplary embodiments,the electrical contact 149 is in a staggered configuration. Because theelectrode 143 is between the semiconductor 146 and the dielectric layer108, the electrode 143 is in a coplanar configuration in these variousexemplary embodiments.

Also, in various exemplary embodiments, an encapsulant 145 is located ina space between two or more portions of the via layer 144. Accordingly,FIG. 4 illustrates an exemplary embodiment of an electronic device 140with a hybrid configuration.

In various exemplary embodiments, the gate electrode 109 is opaque tocertain forms of radiation.

FIG. 5 is a cross section of another exemplary embodiment of anelectronic device according to this invention. Some of the elements inthis figure are commonly numbered with elements previously discussed inconnection with other figures. A duplicative discussion of thoseelements is omitted for the sake of simplicity. The hybrid electronicdevice 150 includes a via layer portion 154 with a tapered sidewall 158and a via layer portion 144 without a tapered sidewall. In variousexemplary embodiments of the devices and methods according to thisinvention, the tapered sidewall 158 allows for easier deposition of themetal electrode along the sidewall of the via layer 154. In variousexemplary embodiments, both sidewalls of the via layer are tapered.

In various exemplary embodiments, a semiconductor 156 is formed over aportion of the electrode 143 and over a portion of the dielectric layer108, and is over a portion of the via layer portion 154. In variousexemplary embodiments, a electrode 157 is a metallic electrode formedover a portion of the via layer portion 154 and in contact with anelectrical contact 159 which is located over a portion of thesemiconductor 156. In various exemplary embodiments, the electrode 157,the electrical contact 159, the semiconductor 156 and the encapsulant155 have a tapered configuration. Also, in various exemplaryembodiments, the encapsulant 155 is located in the space between the vialayer portion 144 and the via layer portion 154.

In various exemplary embodiments of the devices and methods according tothis invention, the electrode 157 and the electrical contact 159 aremade from the same material. In various exemplary embodiments of thedevices and methods according to this invention, the electrode 157 andthe electrical contact 159 are made from a different material.

FIG. 6 is a cross section of another exemplary embodiment of anelectronic device 140 according to this invention. Some of the elementsin this figure are commonly numbered with elements previously discussedin connection with other figures. A duplicative discussion of thoseelements is omitted for the sake of simplicity. The electronic device140 is a hybrid device and includes a via layer portion 142 that is notself-aligned with the electrode 143. In various exemplary embodiments ofthe devices and methods according to this invention, the via layerportion 142 partially covers the electrode 143, the dielectric layer108, the semiconductor 146, and the electrode 149.

FIGS. 7-13 are cross sections of an electronic device 160 illustratingan exemplary embodiment of a method of manufacturing of an electronicdevice according to this invention. Some of the elements in thesefigures are commonly numbered with elements previously discussed inconnection with other figures. A duplicative discussion of thoseelements is omitted for the sake of simplicity. As shown in FIG. 7, forexample, in various exemplary embodiments of the devices and methodsaccording to this invention, a substrate 110, the electrode 109, thedielectric layer 108 and an electrode 143 are formed. Then, in variousexemplary embodiments of the devices and methods according to thisinvention, and as illustrated in FIG. 8, for example, a photosensitiveliquid via layer 162 is formed over the dielectric layer 108 and theelectrode 143.

In various exemplary embodiments of the devices and methods according tothis invention, irradiation, such as, for instance, ultraviolet light,is shone on the photosensitive liquid via layer 162, the sourceelectrode 143, the dielectric layer 108, and the substrate 110, andelectrode 109. In these exemplary embodiments, the radiation cures thephotosensitive liquid via layer 162. In various exemplary embodiments ofthe methods and devices according to this invention, the radiation isshone from the bottom of the gate electrode 110 as indicated in FIG. 8.This so-called backside exposure allows for the curing of portions ofthe photosensitive liquid via layer 162 that are not blocked by anopaque body. The electrode 109 is, in various exemplary embodiments,opaque. The substrate 110 is, in various exemplary embodiments,transparent to the radiation. Thus, only certain portions of thephotosensitive liquid via layer 162 are subjected to radiation invarious exemplary embodiments as indicated by the arrows that passthrough to the photosensitive liquid via layer 162 from the gateelectrode 109 in FIG. 8.

In various exemplary embodiments of the methods and devices according tothis invention, the electrode 143 and the gate electrode 109 are opaqueto radiation. In these various exemplary embodiments of the methods anddevices according to this invention, a portion of the photosensitiveliquid via layer 162 is located above the electrode 143, or above thegate electrode 109, or both. In these various exemplary embodiments,that portion of the photosensitive liquid via layer 162 is not cured bythe radiation. In these various exemplary embodiments, the electronicdevice 160 is said to be self-aligned.

In various exemplary embodiments of the devices and methods according tothis invention, after curing is performed, some uncured material isremoved as shown, for example, in FIG. 9. In various exemplaryembodiments of the devices and methods according to this invention, thisoccurs, for instance, by solvent washing. Accordingly, in theseexemplary embodiments, the portion of the photosensitive liquid vialayer 162 that is above the source electrode 143 and above the topportion 109 of the gate electrode 110 is uncured. This portion of thephotosensitive liquid via layer 162 is to be removed.

As illustrated in FIG. 9, for example, the resultant structure, in thesevarious exemplary embodiments of the devices and methods of thisinvention, has a gate electrode 110 on which a dielectric layer 108 isformed. An electrode 143 is formed over the dielectric layer 108, andmore than one portion of the via layer 162 is formed and cured over thedielectric layer 108. In these various exemplary embodiments, theportion of the dielectric layer 108 that is covered by the electrode 143and the portion of the dielectric layer 108 that covers the top portion109 of the gate electrode 110 is uncovered and provides a recess in thecured portion of the via layer 162.

In various exemplary embodiments of the devices and methods according tothis invention, and as illustrated in FIG. 10, for example, asemiconductor 146 is formed in a portion of the recess of the via layer162 and covers a portion of the dielectric layer 108 and a portion ofthe electrode 143.

In various exemplary embodiments of the devices and methods according tothis invention, and as illustrated in FIG. 11, for example, a mask 164is formed over a portion of the semiconductor 146 and over the portionof the electrode 143 that is not covered by the semiconductor 146. Invarious exemplary embodiments, the mask 164 is printed. Accordingly, andas illustrated in FIG. 12, in various exemplary embodiments of thedevices and methods of this invention, for example, a metal layer 166 isdeposited over the entire electronic device 160 and covers all portionof the via layer 162, an uncovered portion of the semiconductor 146 andthe print resist 164. The metal layer 166 so deposited constitutes anelectrode. Referring to FIG. 14, in various exemplary embodiments, anelectrical device 190 includes an electrical contact 149 deposited on aportion of the semiconductor layer 146. In various exemplaryembodiments, the metal layer 166 is deposited over the electricalcontact 149.

In various exemplary embodiments of the devices and methods according tothis invention, the metal layer 166 is formed directly over the vialayer 162 and over a portion of the semiconductor 146, for instance, byprinting. In various exemplary embodiments of the devices and methodsaccording to this invention, printing the metal layer 166 avoids using amask such as, for example, the mask 164 illustrated in FIGS. 11-12, thatneeds to be subsequently removed.

In various exemplary embodiments of the devices and methods of thisinvention, and as illustrated in FIGS. 13 and 14, for example, the printresist 164 is removed, thus uncovering the portion of the semiconductor146 that is not covered by the electrode 166 or the electrical contact149 and uncovering the portion of the electrode 143 that is not coveredby the semiconductor 146. In various exemplary embodiments of themethods and devices according to this invention, the resultingstructure, as illustrated in FIGS. 13 and 14, for example, is anelectronic device 160 or 190 with a hybrid configuration where at leasta portion of the electrode 143 is located under the semiconductor 146,and where at least a portion of the electrode 166 is located over thesemiconductor 146.

FIG. 15 is a flow chart describing an exemplary embodiment of a methodof fabrication of an electronic device according to this invention. Invarious exemplary embodiments according to this invention, thefabrication method starts in step S100, then continues to step S150,where a first and second electrical contacts are formed, along with adielectric layer. In various exemplary embodiments according to thisinvention, the dielectric layer is located between the first and thesecond electrical contacts. In various exemplary embodiments accordingto this invention, the first electrical contact is a gate electrode.

In various exemplary embodiments according to this invention, the secondelectrical contact is in a coplanar configuration with the semiconductormaterial.

Next, in step S200, an electrically insulating layer is formed. Invarious exemplary embodiments according to this invention, theelectrically insulating layer is formed over the dielectric layer andthe first electrical contact. Next, in step S250, in various exemplaryembodiments according to this invention, the first and second electricalcontacts, the dielectric layer and a portion of the electricallyinsulating layer are exposed to radiation. In various exemplaryembodiments according to this invention, the radiation comes from theside of the first electrical contact.

In various exemplary embodiments according to this invention, theradiation to which the electrical device is subjected to is ultravioletlight.

Next, in step S300, a portion of the electrically insulating layer thatis not irradiated by the radiation is removed. Next, in step S350, asemiconductor material is provided. In various exemplary embodimentsaccording to this invention, the semiconductor material is provided overa portion of the dielectric layer that is not covered by theelectrically insulating layer.

In various exemplary embodiments according to this invention, removingof the portion of the electrically insulating layer that was notirradiated by the radiation is performed by solvent washing.

In various exemplary embodiments according to this invention, theremoval of the portion of the electrically insulating layer creates atapered wall.

In various exemplary embodiments according to this invention, thesemiconductor material is printed over the portion of the dielectriclayer that is not covered by the electrically insulating layer.

Next, in step S400, a mask is formed. In various exemplary embodimentsaccording to this invention, the mask is formed over the secondelectrical contact and a portion of the semiconductor material. Invarious exemplary embodiments according to this invention, the maskprevents the second electrical contact and a portion of thesemiconductor material from being in contact with any other materialduring subsequent steps of this method.

In various exemplary embodiments according to this invention, the maskis a printed resist.

In various exemplary embodiments according to this invention, where thesemiconductor material is printed, no mask is formed.

Next, in step S450, a third electrical contact is formed. In variousexemplary embodiments according to this invention, the third electricalcontact is formed over at least a portion of the electrically insulatinglayer, the semiconductor material and the mask. Next, in step S500, afourth electrical contact is formed over a portion of the thirdelectrical contact and electrically insulating layer.

In various exemplary embodiments according to this invention, the thirdelectrical contact is formed via vapor deposition.

In various exemplary embodiments according to this invention, the thirdand the fourth electrical contacts are made of the same material.

In various exemplary embodiments according to this invention, step S500is omitted.

Next, in step S550, the mask is removed. In various exemplaryembodiments according to this invention, where the semiconductormaterial is a solution processable semiconductor and is printed and nomask is formed, no mask is removed. Control then proceeds to step S600,where the method ends.

This invention has been described in conjunction with the exemplaryembodiments outlined above. Various alternatives, modifications,variations, and/or improvements, are within the spirit and scope of theinvention whether known or presently unforeseen. Accordingly, theexemplary embodiments of the invention, as set forth above, are intendedto be illustrative, not limiting. Various changes may be made withoutdeparting from the spirit and scope of the invention. Therefore, theinvention is intended to embrace all known or later developedalternatives, modifications, variations and/or improvements.

1. An electronic device, comprising: a first electrical contact; adielectric layer located over the first electrical contact; a secondelectrical contact located over the dielectric layer; a semiconductinglayer located over the second electrical contact; and a third electricalcontact located over the semiconducting layer, and an electrical currentbetween the second and third electrical contacts is controlled by thefirst electrical contact.
 2. The electronic device according to claim 1,wherein the electronic device is a thin-film transistor.
 3. A circuitcomprising a plurality of electronic devices according to claim
 1. 4.The electronic device according to claim 1, wherein the semiconductorlayer is an organic semiconductor.
 5. The electronic device according toclaim 1, further comprising an electrically insulating layer over thesemiconductor layer and not in contact with a portion of the thirdelectrical contact; and a fourth electrical contact over the insulatinglayer and electrically connected to the third electrical contact.
 6. Theelectronic device according to claim 5, wherein the electronic device isa pixel circuit in a display.
 7. A circuit comprising a plurality of theelectronic devices according to claim
 5. 8. The electronic deviceaccording to claim 5, wherein the fourth electrical contact includesindium tin oxide.
 9. The electronic device according to claim 5, whereinthe insulating layer has a tapered sidewall.
 10. The electronic deviceaccording to claim 5, wherein an encapsulant is over the semiconductormaterial.
 11. The electronic device according to claim 1, wherein thesecond and the third electrical contacts include gold.
 12. Theelectronic device according to claim 1, further comprising anelectrically insulating layer aligned to the first electrode and secondelectrode and not in contact with the semiconductor; and a forthelectrical contact over the insulating layer and electrically connectedto the third electrical contact.
 13. The electronic device according toclaim 12, wherein the electronic device is a pixel element in a display.14. A circuit comprising a plurality of the electronic devices accordingto claim
 12. 15. The electronic device according to claim 12, whereinthe fourth electrical contact includes indium tin oxide.
 16. Theelectronic device according to claim 12, wherein the insulating layerhas a tapered sidewall.
 17. The electronic device according to claim 12,wherein an encapsulant is over the semiconductor material.